GEOLOGY 



THE DESERT OF SAHARA. 



THE following summary in respect to Sahara is translated from Karl 

 Arenz's review of the researches of Earth, Overweg, Richardson, and 

 Vogel : 



The Desert of Sahara has been represented as a low, flat plain, scarcely 

 rising above the level of the ocean; a vast sea of sand, upon which, besides 

 a few craggy lines of rock that project into it here and there, there are no 

 other elevations but those shifting mounds and columns of sand that, like 

 huge billows, move at the mercy of the wind; a trackless waste, where the 

 traveller, after many days' journey, may still look in vain for a single trace 

 either of vegetation or of animal life. Modern researches, however, do not 

 sustain this view. On the contrary, they show beyond a doubt that the 

 Sahara consists mostly of a series of table-lands of a greater or less eleva- 

 tion, jutting up occasionally into mountains, and sometimes divided from 

 each other by valleys, or plains covered with sand, and apparently inter- 

 minable. Let us take a rapid survey of the principal results bearing upon 

 this point. 



On their way from the shore of the Mediterranean to Ghat, Earth's party 

 crossed three high and wide plateaus, parallel with the Mediterranean coast. 

 First, came the Gharian plateau, 2000 feet high where first they ascended 

 it, but gradually sloping as they passed on, until it terminated at the moder- 

 ate height of only 500 feet. Next, the monotonous Hamadah, stretch- 

 ing away at a uniform height of from 1300 to 1600 feet, for 120 miles; 

 and then, after crossing Wadys of 600 to 700 feet elevation, and miniature 

 deserts of 1000 feet, the travellers reached the third, or the Murzuk plateau. 

 This plateau is elevated not far from 1500 feet above the level of the ocean. 

 Its lowest depression is 900 to 1000 feet high, while other portions attain a 

 height of 1800 to 2200. After leaving the Murzuk plateau, the caravan, as 

 it went toward Ghat, appears to have found a mean altitude of 1250 to 

 1450 feet; and so likewise for some distance to the southward of Ghat, until 

 it came to the wild, mountainous region which lies between Ghat and Air, 

 where it entered a Wady (Adschunscher) lying at a height of 2956 feet, and 

 situated amid mountain peaks that were roughly estimated as about 4000 

 feet high. From Tin Tellust in Air, the altitude of the region was estimated 

 at 18i)4 feet, nor can we suppose the southern Hamadah to lie at a much 

 greater depression. 



